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Chapter 4 Measurement
4.3 Before Measurement
This section describes notes on accuracy and the handling of the Rogowski
Coil Sensor part when measuring the current using this instrument.
4.3.1 To Achieve Accurate Measurement
As explained in Chapter 3 "Measurement Principle," the Rogowski Coil is a
wire rod wound tight around a tube-like wick material, as illustrated in Figure
3.1. The coil formed into a ring body detects a change in magnetic flux
caused by the current passing through the inside of the coil. The evenly
wound coil causes no error even when the current to be measured does not
flow through the center of the coil. In addition, each turn of coil enables the
cancellation of external magnetic fields.
Note that the uniformity of the Rogowski Coil is slightly disturbed at the
Rogowski Coil connection part on the joint hole, which is designed to
maintain the coil as a ring body. The area around this part is not suited to
measure current. In addition, the coil cannot sufficiently cancel a magnetic
field produced by external current flowing through in the vicinity of this part.
This instrument is calibrated by current that flows through the center of the
Rogowski Coil. Avoid measuring current in the vicinity of the joint hole as
much as possible in order to achieve accurate measurement. It is
recommended to measure current at the center of the Rogowski Coil.
For reference, Figure 4.3 shows the position of the connection part of the
Rogowski Coil.
Figure 4.3 Rogowski Coil Connection Part
The connection part of the Rogowski Coil is in the center of the dotted circle.
It is known that a larger measurement error is caused as the current to be
measured comes closer to this part. Avoid measuring current in the dotted
area, because a measurement error of −4% or more may be caused by the
measurement performed in the area. In addition, the coil cannot sufficiently
cancel the magnetic flux produced by external current. Before measuring
current, place conductors in which current flows other than the conductor to
be measured away from the Rogowski Coil connection part as much as
possible.
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